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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_262</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_261.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_262</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_263.html">next page ></a></td> </tr> <tr> <td id="ebook_page" align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 262</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">the error terms <i>E</i></font><font face="Times New Roman, Times, Serif" size="1"><sub>cm</sub></font><font face="Times New Roman, Times, Serif" size="3"> and <i>E</i></font><i><font face="Times New Roman, Times, Serif" size="1"><sub>i</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3"> are small and might be considered for deletion.</font><font face="Times New Roman, Times, Serif" size="2"><sup>**</sup></font><font face="Times New Roman, Times, Serif" size="3"> If, in addition, the code multipath is modeled as white noise, then the design model reduces to</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="d7d0982bf849e9c074e37270ddf6ea99.gif" border="0" alt="0262-01.GIF" width="359" height="39" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="e32637cf505441264d8b9c133185892f.gif" border="0" alt="0262-02.GIF" width="375" height="40" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">where the state and model definitions were discussed in the previous section. This model could be implemented directly [23, 71, 72]. It has been suggested that the integer ambiguities could be determined from the value of x</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>N</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> when two conditions are satisfied. First, the error variance of x</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>N</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> must be significantly less that 1. Second, the value of x</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>N</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> must be near an integer value [71, 72]. Some experimental implementations have, however, demonstrated difficulties with the approach [52, 89] because of selection of incorrect integers. Such difficulties are explained in the following example.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Example This example continues the single-dimensional inertial-frame GPS-aided-INS example from the previous subsection. The truth model includes the INS error state, a code multipath error state, and an integer ambiguity. The model parameters for each state are defined in the example of the previous section. The design model deletes the code multipath state and uses <img src="8045a56c57c3b1bed540644a83c55040.gif" border="0" alt="C0262-01.GIF" width="44" height="17" />, which is the sum of the variances of the code multipath and measurement noise. The actual performance is determined with the covariance analysis techniques defined in Sec. 4.4.2. The filter's estimate of its performance is based on the covariance matrix internally calculated by the reduced order Kalman filter.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Figure 7.11 shows the error standard deviation of the position and integer ambiguity states. Both the actual and filter estimate of performance are plotted in the left column. The right column shows the filter gains. The filter neglects the time correlation of the multipath error. Therefore the ambiguity estimation gains are initially high, but rapidly decrease toward zero. After 2 min, the gains are essentially zero, since, based on the design model, 120 independent measurements of <i>N</i> have been averaged. In fact, 120 correlated measurements have been averaged. Therefore the variance of <img src="cd72d36d8924060834c8f78c59935613.gif" border="0" alt="NCIRC.GIF" width="13" height="14" /> is much larger than the variance calculated by the filter. If the value of <img src="cd72d36d8924060834c8f78c59935613.gif" border="0" alt="NCIRC.GIF" width="13" height="14" /> were fixed at any time during this simulation based on <img src="241753eb0ba89a7bef1210a3d400551f.gif" border="0" alt="C0262-02.GIF" width="19" height="17" />'s being small, there is a very good chance that the fixed value of <img src="cd72d36d8924060834c8f78c59935613.gif" border="0" alt="NCIRC.GIF" width="13" height="14" /> would be incorrect. The experimental difficulties are therefore predicted in Fig. 7.11.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">The filter does not model any driving noise on the state representing the integer ambiguity. This modeling decision is based on the knowledge that the actual integer ambiguity is a constant integer value. Since there is no process noise driving the integer ambiguity states, the filter gains for the ambiguities asymptotically approach zero. The filter is also not aware of the multipath measurement errors. The implemented</font><font face="Times New Roman, Times, Serif" size="2" color="#FFFF00"></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3" height="1"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2"><sup>** </sup>All such assumptions should be analyzed for validity relative to the conditions of a given application.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_261.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_262</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_263.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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